1. Field of This Invention
This invention relates to double wall heat exchangers and methods of preparing such double wall heat exchangers.
2. Prior Art
Due to the possible toxicity of solar fluids, several codes of state and local governments have been enacted which require the heat exchanger tube coil to have two separate walls. The design of such double wall heat exchangers can be of two basic types, namely, vented and unvented. With the vented design, a failure of the inner coil will cause leakage at the terminal ends of the coil at a specified pressure (about 10 psig) between the tubes. With the unvented design, the terminal ends of the coil are sealed. The placing of one tube inside of another has been done in the past; however, in such cases, there is little or no metal contact surface between the tube walls resulting in poor heat transfer. The art has tried more elaborate schemes which have also been unsatisfactory.